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PSY280H1 (49)

chap 9 textbook notes

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Kristie Dukewich

CH9PERCEIVING COLOR Introduction to ColorSELECTIVE TRANSMISSIONonly some wavelength pass through the TRANSPARENT OBJECTS or substancesSome functions of color visionFacilitate perceptual organizationgroup elements GestaltDetermines colors of transparent objects such as liquids oo Allow object discrimination pick out objects in scenes plastic glass ex cranberry juice selectively transmitbc enhances contrast of objects thats similar in grayscale longwavelength lightappears red o Evolutionary reason color visioncolored foods detection ability o ADDITIVE COLOR MIXTURE mixing Lightwhen colored lightssuggested reason for color vision in monkeyhumans superimposed all the light that is reflect from the surface by each light when alone is also reflected when the lights are superimposedex picking berries easier w color visionSummed together light contains all the wavelength from one o Recognizeidentify things easier color combined with all the wavelength from the other colorEx pink banana identification longer time than yellow bananaWhat colors do we perceive o Can describe all perceivable colors w red yellow green bluecombinations of these 4 termsMinimal amount of colors need to describe spectrumOther colors orange violet purple brown not needed o EXTRASPECTRAL COLORScolors that do not appear in the spectrumEx brownmix of redorange or yellowblack purplemix of redblue o SATURATIONaccess additional colors by addingremoving white ie changing the colors saturationAdding whiteadding equal amounts to all wavelengths across the spectrum decrease saturation DESATURATED o Change wavelength intensity saturationdiscriminable colorsColor and wavelength o Perception of color associated w physical property of wavelengthVisible spectrum from short wavelength 400nm to longwavelength 700nm Wavelength bands wi the range associated w diff colors o SUBTRACTIVE COLOR MIXTURE mixing paintwhen paints mixed both paints still absorb the same wavelength they absorbed when400 nm450 nmviolet 575 nm590 nmyellow alone so the only wavelength reflect are those that are reflected by450 nm490 nmblue 590 nm620 nmorange both paints in common500 nm575 nmgreen620 nm700 nmredSummed together paint absorbs all the wavelength from one color and all the wavelength from the other coloro Reflection and TransmissionCOLORS OF LIGHT in spectrum related to their spectrumColors of object related to wavelengths of light reflected from the objects into eyesREFLECTANCE CURVESplots of percentage of light reflected vs wavelengthNote whiteblack paper reflect all wavelength equally Note some objects reflect a dominate wavelength Wavelength do not have color o Colors are created by our perceptual system bc we relate specific colors to specific wavelengthsConnection btwn wavelength and the experience called color is arbitrary o Light rays are simply energy nothing intrinsically colored about wavelengths not physical property of an objectNewtonTrichromatic theory of color visionTRICHROMATIC THEORY OF COLOR VISIONcolor vision depends on the activity of three different receptor mechanisms o Proposed by Thomas YoungHermann von HelmholtzYoung 1802 proposed the theory based on findings that ppl w normal vision need at least 3 wavelengths to match any wavelengths in Test FieldLater championedrefined by HelmholtzNamed YOUNGHELMHOLTZ THEORY OF COLOR VISIONo based on results of psychophysical procedure COLOR MATCHINGCHROMATIC COLORS HUESsome wavelengths of OPAQUE o Central idea color vision depends on three receptor mechanisms OBJECTS are reflected more than others each w different spectral sensitivitiesex the hue chromatic color of tomato is redLight of particular wavelength stimulates 3 receptorSELECTIVE REFLECTIONproperty of opaque objects that mechanisms in different degrees reflect some wavelength more than others characteristicPattern of activity in 3 mechanisms result in perception of color of chromatic colorsEach wavelength represented in nervous system by own patternACHROMATIC COLORSwhen reflection similar across of activity in the 3 receptor mechanisms full spectrum ie no hue as w black gray white colors
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